Wellbore cleaning efficiency monitoring

ABSTRACT

A system includes a measuring device configured to receive a returned mud mixture from a riser and to direct the returned mud mixture to a mud processing system. The measuring device includes a duct, a first load cell coupled to the duct, and a mud level sensor. The duct has a first end disposed at a first level and a second end disposed at a second level lower than the first level. The first load cell is configured to determine a mass of a quantity of the returned mud mixture within the duct during a drilling operation. The mud level sensor is configured to determine a height of the returned mud mixture in the duct. The mass of the quantity of the returned mud mixture may be used to determine a density of the quantity of the returned mud mixture and a cleaning efficiency ratio of the drilling operation.

BACKGROUND

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

Advances in the petroleum industry have allowed access to oil and gas drilling locations and reservoirs that were previously inaccessible due to technological limitations. For example, technological advances have allowed drilling of offshore wells at increasing water depths and in increasingly harsh environments, permitting oil and gas resource owners to successfully drill for otherwise inaccessible energy resources. Directional drilling has also increased the ability to access some types of energy resources with fewer wells and/or from alternative surface locations. During drilling operations, a drilling end of a drill string extracts portions of a downhole formation to progress the drill string further downhole. A drilling mud mixture may be directed downhole for a variety of purposes, such as to facilitate removal of the extracted portions of the downhole formation, to control the pressure within the well, to drive a drill motor, or to cool or lubricate portions of the drill string, among others. However, changes in the downhole environment, such as changes in the drilling formation, changes of the drill string, and/or changes of the drilling mud directed downhole may affect the removal of the extracted portions of the downhole formation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of an offshore platform and a well;

FIG. 2 illustrates an embodiment of a drilling system with a mud monitoring system and a mud processing system;

FIG. 3 illustrates an embodiment of the mud monitoring system of FIG. 2;

FIG. 4 illustrates an embodiment of the mud monitoring system of FIG. 2;

FIG. 5 illustrates an embodiment of the mud monitoring system of FIG. 2;

FIG. 6 illustrates an embodiment of the mud monitoring system of FIG. 2; and

FIG. 7 illustrates an embodiment of method of monitoring returned mud of the drilling system.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers'specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Systems and techniques for monitoring a returned mud flow from a wellbore during a drilling operation from a land-based platform or an offshore platform are set forth below. An offshore platform may include, but is not limited to a drillship, a semi-submersible platform, a floating production system, or the like. During drilling operations, a drilling mud is directed downhole toward a bottom hole assembly (BHA) of a drill string for cooling of the drill string, lubrication of the drill string, pressure control of the wellbore, and/or removal of extracted portions of the formation, among other functions. It is desirable to remove the extracted portions (e.g., cuttings) of the formation at approximately the same rate as the cuttings are generated downhole by the BHA of the drill string. Accumulation of the extracted portions of the formation downhole may decrease drilling performance or prevent subsequent removal of the BHA from the downhole environment. Removing the extracted portions from the downhole environment to the drilling platform at the surface may facilitate a desired rate of penetration (ROP) of the BHA through the formation. Some formations may be prone to erosion (e.g., washout), such that circulation of the drilling mud along the drill string may extract additional portions of the formation that radially surround the BHA. That is, the bore may be enlarged beyond a diameter of the BHA. Enlarged portions of the bore may reduce the flow or circulation of drilling mud or other fluids (e.g., cement, hydrocarbons) within the bore. Reducing or eliminating washouts and the effects of washouts may improve the control of the direction of the bore, may improve well pressure control, and/or may decrease pipe sticking events. Additionally, or in the alternative, reducing or eliminating washouts may improve the quality of subsequent casing of the bore and/or may decrease the quantity of cement for the subsequent casing.

As discussed herein, a cleaning efficiency ratio of the drilling operation may be determined through monitoring the drilling mud at the surface between the riser and mud processing systems. The cleaning efficiency ratio is a ratio of the cuttings returned with the drilling mud relative to the cuttings generated by the BHA. Measurements, such as Coriolis flow measurements, of the returned mud mixture while the mud mixture is within the riser may be negatively affected by different phases (e.g., liquid, solid, gas) within the returned drilling mud flow. Measurements of the returned mud within the mud processing system (e.g., shaker tables) may inaccurately estimate the mass of the returned cuttings. Measurement of the cuttings returned prior to separation of the cuttings from the drilling mud may improve the accuracy of the mass measurements of the cuttings, and therefore the accuracy of the determined cleaning efficiency ratio. The determined cleaning efficiency ratio may be used to control the mud supplied to the BHA and/or the performance of the BHA downhole. In some embodiments, the maintenance of the cleaning efficiency ratio near 1.0 may improve the quality (straightness, directionality, diameter) of the bore, thereby reducing costs.

With the foregoing in mind, FIG. 1 illustrates an offshore vessel 10 as an embodiment of a drilling platform of a drilling system 30. Although the presently illustrated embodiment of an offshore vessel 10 is a drillship (e.g., a ship equipped with a drill rig and engaged in offshore oil and gas exploration and/or well maintenance or completion work including, but not limited to, casing and tubing installation, subsea tree installations, and well capping), other offshore platforms such as a semi-submersible platform, a floating production system, or the like may be substituted for the drillship. Indeed, while the techniques and systems of the mud monitoring system described below may be utilized on a drillship, the techniques and systems are intended to cover at least the additional offshore platforms described above, as well as land-based platforms of drilling systems 30.

As illustrated in FIG. 1, the offshore vessel 10, with a derrick 11 thereon, includes a riser 12 extending therefrom. The riser 12 may include a pipe or a series of pipes (e.g., riser joints) that connect the offshore vessel 10 to the seafloor 14 via, for example, blow out preventer (BOP) 16 that is coupled to a wellhead 18 on the seafloor 14. In some embodiments, the riser 12 may transport produced hydrocarbons and/or production materials between the offshore vessel 10 and the wellhead 18, while the BOP 16 may include at least one valve with a sealing element to control wellbore fluid flows. In some embodiments, the riser 12 may pass through an opening (e.g., a moonpool) in the offshore vessel 10 and may be coupled to drilling equipment of the offshore vessel 10. As illustrated in FIG. 1, it may be desirable to have the riser 12 positioned in a vertical orientation between the wellhead 18 and the offshore vessel 10, for example, to allow a drill string 19 made up of drill pipes to pass from the offshore vessel 10 through the BOP 16 and the wellhead 18 and into a wellbore 22 within a formation 20 below the wellhead 18.

A bottom hole assembly (BHA) 24 coupled to the drill string 19 forms the wellbore 22 within the formation 20. The BHA 24 is coupled to the distal end of the drill string 19. The BHA 24 may include, but is not limited to a drill bit, mud motor, reamer, and/or stabilizer, among other components. The drill string 19 may rotate, thereby causing one or more components of the BHA 24 to rotate and penetrate into the formation, axially enlarging an end 26 of the wellbore 22. Additionally or in the alternative to rotation of the drill string 19, the one or more components of the BHA 24 may rotate. For example, a fluid (e.g., drilling mud) supplied through the drill string 19 to a mud motor of the BHA 24 may cause rotation of a drill bit of the BHA 24. The penetration rate of the BHA 24 through the formation 20 may be based on multiple factors, such as the type of the formation 20, the weight on the bit (WOB) of the BHA 24, and the mud flow rate, among others. The drilling mud may be supplied from the offshore vessel 10 on the ocean surface through the drill string 19 to the BHA 24 and into the wellbore 22. The drilling mud may circulate within the wellbore 22 and be returned to the offshore vessel 10 on the ocean surface via an annulus between the wellbore 22 and the drill string 19. Within the riser 12 above the wellhead 18, the drilling mud may be returned to the offshore vessel 10 via an annulus between the riser 12 and the drill string 19.

FIG. 2 illustrates an embodiment of a drilling system 30 that supplies a drilling mud 36 to the BHA 24. The drilling system 30 may be an embodiment of the offshore vessel 10 described above with FIG. 1, or a land-based platform. The drilling system 30 includes a mud monitoring system 32, a mud processing system 34, and a mud pump 38. The mud pump 38 directs the drilling mud 36 into the drill string 19 toward the BHA 24. A controller 140 may control the mud pump 38 to control the flow rate from the mud pump 38. The flow of the mud 36 through a mud motor 40 of the BHA 24 may cause rotation of the BHA 24, as shown by an arrow 42. FIG. 2 illustrates one BHA 24 with different conditions within the wellbore 22 around the BHA 24. As discussed in detail below, it is appreciated that one BHA 24 may be coupled to the drill string 19 at a time. Through rotation of a drill bit 44 of the BHA 24, fragments 48 of the formation 20 may be removed as the drill bit 44 interfaces with the end 26 of the wellbore 22. Furthermore, a shoulder 46 of the drill bit 44 and/or reamers or stabilizers of the BHA 24 may also remove fragments 48 of the formation 20. These removed fragments 48 (e.g., cuttings) from the formation 20 enlarge the wellbore 22 and enable the BHA 24 and the drill string 19 to progress further into the formation 20.

The drilling mud 36 may exit through the drill bit 44 or other portions of the BHA 24 into an annulus 50 between the BHA 24 and the wellbore 22. Within the annulus 50, the cuttings 48 may be entrained or carried with the drilling mud 36. The arrows 52 illustrate a returned mud mixture with the drilling mud 36 and the cuttings 48. The drilling system 30 circulates the mud 36 downhole to the BHA 24 through the drill string 19, and returns the mud mixture 52 to a surface 55 of the drilling system 30 through the riser 12. As discussed herein, the surface 55 includes locations where the returned mud mixture 52 may be processed, such as the offshore vessel 10 on the sea surface or the land-based platform. The mud monitoring system 32, the mud processing system 34, and the mud motor 38 may be disposed at the surface 55 of the drilling system 30, as illustrated in FIG. 2. In some embodiments, a top drive system 53 or rotary table at the surface 55 of the drilling system 30 may rotate the riser 12 and/or the drill string within the formation 20. The top drive system 53 may be a portion of the derrick 11 of the offshore vessel 10 or land-based platform at the surface 55. The controller 140 may control the top drive system 53. A first portion of the riser 12 and a second portion of the drill string 19 may be within the derrick 11 of the drilling system 30 at the surface 55.

At the surface 55 of drilling system 30, the returned mud mixture 52 may be routed through a return line 54 and a duct 56 of the mud monitoring system 32. As discussed in detail below, the mud monitoring system 32 may determine a density of a quantity of the returned mud mixture 52, and determine a cleaning efficiency ratio for the drilling operation. The returned mud mixture 52 may be directed to the mud processing system 34 via a drain 58. A shaker 60 or other device of the mud processing system 34 may remove the cuttings 48 from the returned mud mixture 52. Additional mud cleaning equipment 62 may remove particulates and/or fluids (e.g., water, hydrocarbons) from the returned mud mixture 52, resulting in a cleaned mud 36. The cleaned mud 36 may be directed to a mud pit 64 or reservoir for future use via the mud pump 38. One or more mud additives 65 (e.g., water, oil, fluids, solids, proppants) may be added to the cleaned mud 36 prior to subsequent delivery of the drilling mud 36 to the drill string 19 via the mud pumps 38. In some embodiments, the controller 140 may control the composition of the drilling mud 36 delivered to the drill string 19 via control of the one or more mud additives 65. In some embodiments, the controller 140 may provide suggested changes to the composition of the drilling mud 36 for one or more operators of the drilling system 30 to consider. In some embodiments, the mud monitoring system 32, the mud processing system 34, and the controller 140 may be disposed at the surface 55 of the drilling system 30 apart from the derrick 11 where the riser 12 and drill string 19 reach the surface 55. For example, the return line 54 at the surface 55 may extend from the riser 12 toward the mud monitoring system 32.

The mud monitoring system 32 is disposed between the riser 12 and the mud processing system 34 of the drilling system 30. The mud monitoring system 32 may determine the mass of a quantity of the returned mud mixture 52 within the duct 56 of the mud monitoring system 32, thereby facilitating the determination of the density of the returned mud mixture 52, which may be used to determine the cleaning efficiency ratio η during the drilling operation. The mud monitoring system 32 is disposed at the surface of the land-based platform or offshore platform 10, thereby enabling the components of the mud monitoring system 32 to be maintained, calibrated, and/or replaced more easily than sensors within the drill string or riser, such as sensors of the BHA 24 within the wellbore 22. Moreover, through determination of the density of the quantity of the returned mud mixture, the mud monitoring system 32 may more accurately measure two-phase flows than Coriolis flow meters of the return line. Additionally, a measuring device disposed upstream of the mud processing system 34 may enable the mud monitoring system 32 to better account for effects of the porosity of the cuttings 48 than measurement of cuttings after elements (e.g., shakers) of the mud processing system 34.

While some wellbores 22 may be drilled substantially along a vertical axis 68, some wellbores 22 have one or more portions 66 that deviate from the vertical axis 68. Additionally, some sections 70 of the wellbore 22 may extend horizontally. As discussed herein, the horizontal sections 70 may extend in a direction that is within 10, 20, or 30 degrees of a horizontal axis 72. The angle of the wellbore 22, the mud flow rate, the mud composition, the mud viscosity, and the density of the mud 36 that flows into the annulus 50 affects how the cuttings 48 are entrained in the returned mud mixture 52 that returns to the surface 55. Additionally, the composition of the cuttings, the density of the cuttings, the wellbore pressure, and produced fluids (e.g., water, hydrocarbons) from the wellbore 22 may affect how the cuttings 48 are entrained in the returned mud mixture 52 that returns to the surface 55. As discussed herein, the cleaning efficiency ratio (η) is a ratio of the cuttings removed from the wellbore relative to the cuttings generated from the wellbore. An accumulation of cuttings 48 in the wellbore 22 may occur when the cleaning efficiency ratio is less than 1.0, such as shown in the first example 74 of the BHA 24 in FIG. 2. An accumulation of cuttings 48 may decrease drilling performance (e.g., rate of penetration, cutting efficiency, drill bit lifetime). Additionally, a packed accumulation of cuttings 48 may contribute to a stuck pipe condition that prevents or hinders subsequent removal of the BHA 24 from the wellbore 22.

The second example 76 of the BHA 24 in FIG. 2 illustrates a washout condition of the wellbore 22. Some formations 20, such as sandy formations and/or porous formations, may be prone to erosion that will generate cuttings 48 in addition to those generated by engagement of the drill bit 44 with the end 26 of the wellbore 22. For example, the flow of drilling mud 36 out of the drill bit 44 may erode fragments from the formation 20, thereby enlarging the wellbore 22 as shown with an enlarged section 78 of the wellbore 22 in the second example 76. These eroded fragments of the formation 20 may be entrained in the returned mud mixture 52 with the cuttings 48 from the end 26, and returned to the surface 55. Accordingly, the cleaning efficiency ratio during a washout condition may increase to be greater than 1.0. That is, the cuttings extracted from the wellbore 22 are greater than the cuttings expected to be generated by the engagement of the drill bit 44 with the end 26 of the wellbore 22.

FIG. 3 illustrates an embodiment of the mud monitoring system 32 of FIG. 2. The return line 54 directs the returned mud mixture 52 to the duct 56 of the mud monitoring system 32. The returned mud mixture 52 flows toward the surface 55 through the riser 12 along the vertical axis 68, then in a lateral direction 90 along the return line 54 and the duct 56. The return line 54 and the duct 56 of the mud monitoring system 32 are disposed on the surface, which may include on a land-based production platform or an offshore vessel 10. In some embodiments, the duct 56 is an open duct 92, or trough, such that the returned mud mixture 52 within the trough 92 is at atmospheric pressure at the surface 55 of the drilling system 30. In some embodiments, the duct 56 is fixedly supported along its length 100 between a first end 94 and a second end 96, as shown in FIG. 3. The returned mud mixture 52 is directed into the duct 56 at or near the first end 94, which is at an elevation 98 relative to the second end 96. The elevation 98 between the first end 94 and the second end 96 may facilitate a flow of the returned mud mixture 52 toward the drain 58 at the second end 96.

The length 100 of the duct 56 may be selected to reduce or eliminate a turbulent or unsteady flow and/or fluid height at a measurement position along the duct 56. Flow dynamics of the returned mud mixture 52 can affect the measured fluid mass and/or the measured depth. For example, the flow regime (e.g., laminar/turbulent) at a position along the length 100, the flow rate of the returned mud mixture 52, and/or the friction losses of the returned mud mixture 52 in the duct 56 may affect pressure or mass measurements of the returned mud mixture 52 at the respective position along the length 100 of the duct 56. To reduce or eliminate noise, a sensor of a measuring device 102 may be disposed at a position that is a critical length downstream from the first end 94, where the critical length is selected due to a substantially reduced or eliminated measurement noise caused by the entry of the returned mud mixture 52 into the duct 56 near the first end 94. For example, a load cell 104 of the measuring device 102 may be disposed as a sensor at a first position 112 along the length 100 of the duct 56, where the first position 112 is spaced a distance 114 from the return line 54. The distance 114 may be approximately 25 to 90 percent, 40 to 75 percent, or 50 percent of the length 100 of the duct 56.

The measuring device 102 may be disposed at one or more positions along the duct 56 to provide one or more inputs that facilitate the determination of a volume and a density of a quantity 106 of the returned mud mixture 52. The load cell 104 of the measuring device 102 may be configured to determine a mass of the quantity 106 of the returned mud mixture 52 at the first position 112 within the duct 56. In some embodiments, the load cell 104 may be configured to determine a weight of the quantity 106 of the returned mud mixture 52, and the mass of the quantity 106 may be determined therefrom. A mud level sensor 108 of the measuring device 102 may determine a height 110 of the quantity 106 of the returned mud mixture 52. The mud level sensor 108 may be positioned at a second position 116 along the length 100 of the duct 56. In some embodiments, an offset 118 between the first position 112 and the second position 116 may be between 0 percent (i.e., no offset) of the length 100 and 10 percent of the length 100 of the duct 56.

The load cell 104 may include, but is not limited to one or more strain gauges coupled to the duct 56 at the first position 112 along the length 100 of the duct 56. In some embodiments, the load cell 104 is a hydraulic gauge or a pneumatic gauge. The quantity 106 of the returned mud mixture 52 may be a column with a volume defined by an area of the load cell 104 and the height 110 between a surface 126 of the returned mud mixture 52 and the load cell 104. The fixed supports at the ends 94, 96 of the duct 56 may reduce the deflection and/or vibration of the duct 56 due to the flow of the returned mud mixture 52, thereby increasing the ability of the load cell 104 to accurately measure the mass of the quantity 106 of the returned mud mixture 52. That is, the fixed supports at the ends 94, 96 of the duct 96 may reduce noise of the output of the load cell 104. In some embodiments, the load cell 104 is positioned at a bottom surface 120 of the duct 56, as shown in the transverse section of FIG. 3. The duct 56 may have various shapes including, but not limited to, the trough shape 122 illustrated in FIG. 3, a curved shape, a semicircular shape, an elliptical shape, a rectangular shape, and so forth. The shape of the duct 56 and the elevation 98 of the duct 56 may facilitate the continuous flow of the returned mud mixture 52 from the return line 54 toward the drain 58. In some embodiments, a cleaning valve 146 (e.g., solenoid valve) may be controlled to direct a pressurized flow of a fluid (e.g., mud 36, water, fresh water-based cleaning solution) across the load cell 104 to reduce or eliminate buildup of the returned mud mixture 52 with its entrained cuttings 48. In some embodiments, the controller 140 may actuate the cleaning valve 146, such as periodically prior to measurement periods of the load cell 104.

In some embodiments, the mud level sensor 108 of the measuring device 102 includes a paddle 124 configured to float at a surface 126 of the returned mud mixture 52 in the duct 56. The paddle 124 may be coupled to an arm 128 and a sensor 132 (e.g., potentiometer, rotation sensor, rotary encoder), such that an angle 134 of the arm 128 relative to an axis (e.g., vertical axis 68) is based on a depth 130 of the returned mud mixture 52 in the duct 56 at the position of the paddle 124. For example, the angle 134 may increase as the depth 130 increases, and the angle 134 may decrease as the depth 130 decreases. Other mud level sensors 108 may include, but are not limited to non-contact sensors (e.g., ultrasonic sensors, microwave sensors), capacitance sensors, and float sensors, among others.

The load cell 104 and the mud level sensor 108 of the measuring device 102 may be coupled to a controller 140. A processor 142 of the controller 140 may execute instructions stored on a memory 144 of the controller 140 to monitor the returned mud mixture 52 in the duct 56. The controller 140 is configured to determine a mass of the quantity 106 of the returned mud mixture 52 based on feedback from the load cell 104. The mass (m_(quantity)) of the quantity 106 of the returned mud mixture 52 may be determined by Equation (1):

$\begin{matrix} {m_{quantity} = {P_{static}\frac{A_{{load}\mspace{14mu} {cell}}}{g}}} & {{Equation}\mspace{14mu} (1)} \end{matrix}$

where P_(static) is the fluid static pressure of the returned mud mixture 52 measured by the load cell 104, A_(load cell) is the area of the load cell 104, and g is the gravitational acceleration.

The controller 140 may also be configured to determine the height 110 of the quantity 106 of the returned mud mixture 52 based on feedback from the mud level sensor 108. For example, if the second position 116 of the mud level sensor 108 is the first position 112 of the load cell 104, the depth 130 at the mud level sensor 108 may be approximately the same as the height 110. Additionally, or in the alternative, the controller 140 may be configured to determine the height of the quantity 106 of the returned mud mixture 52 based at least in part on the depth 130, the elevation 98, and the length 100 of the duct 56. Using the determined mass m_(quantity) of the quantity 106 of the returned mud mixture 52, the controller 140 may determine a density of the quantity 106 of the returned mud mixture 52. For example, the controller 140 may be configured to determine the density (ρ_(mixture)) of the returned mud mixture 52 by Equation (2):

$\begin{matrix} {\rho_{mixture} = \frac{m_{quantity}}{A_{{load}\mspace{14mu} {cell}}*h}} & {{Equation}\mspace{14mu} (2)} \end{matrix}$

where m_(quantity) is the determined mass of the quantity 106 of the returned mud mixture 52, A_(load cell) is the area of the load cell 104, and h is the depth of the quantity 106 of the returned mud mixture 52 at the load cell 104. That is, the density (ρ_(mixture)) of the returned mud mixture 52 may be determined by dividing the mass m_(quantity) of the quantity 106 of the returned mud mixture 52 by the volume of the quantity 106, where the volume may be determined as the product of the base area of the quantity 106 with the height 110 of the quantity 106. For the mud level sensor 108 of FIG. 3 with the arm 128 and the paddle 124, the density ρ_(mixture) of the returned mud mixture 52 may be determined by Equation (3):

$\begin{matrix} {\rho_{mixture} = \frac{m_{quantity}}{A_{{load}\mspace{14mu} {cell}}*\left( {h_{duct} + h_{sensor} - {l_{arm}*{\cos (\theta)}}} \right)}} & {{Equation}\mspace{14mu} (3)} \end{matrix}$

where m_(quantity) is the determined mass of the quantity 106 of the returned mud mixture 52, A_(load cell) is the area of the load cell 104, and h_(duct) is the height 111 of the duct 92, h_(sensor) is a displacement 113 of the rotation sensor 132 above a top 115 of the duct 92, l_(arm) is a length of the arm 128, and θ is the angle 134. The depth 130 at the mud level sensor 108 is evaluated with the parenthetical value (h_(duct)+h_(sensor)−l_(arm)*cos(θ)) of Equation (3), which may be approximately the same as the height 110 of the quantity 106 if the mud level sensor 108 is positioned appropriately with respect to the load cell 104.

The returned mud mixture 52 includes the mud 36 and entrained cuttings 48. Accordingly, the mass (m_(quantity)) of the quantity 106 of the returned mud mixture 52 is a sum of the mass (m_(mud)) of the returned mud 36 in the quantity 106 and the mass (m_(cuttings)) of the cuttings 48 in the quantity 106. Properties of the mud 36 routed to the BHA 24, such as the density (ρ_(mud)) and viscosity of the mud, are known to the controller 140. Furthermore, some known properties of the drilling mud 36 routed to the BHA 24 may be controlled to affect the ability of the mud 36 to lift the cuttings 48 to the surface and to control the pressure in the wellbore 22.

With the density ρ_(mud) of the drilling mud 36 and the determined density ρ_(mixture) of the returned mud mixture 52, the controller 140 may determine a cleaning efficiency ratio η that reflects the returned cuttings relative to the expected cuttings. The cleaning efficiency ratio η may be determined utilizing the following Equation (4):

$\begin{matrix} {\eta = {\frac{\rho_{mixture} - \rho_{mud}}{\rho_{cuttings} - \rho_{mud}}*\frac{Q_{mud}}{{ROP}_{lag}*A_{wellbore}}}} & {{Equation}\mspace{14mu} (4)} \end{matrix}$

where ρ_(mixture) is the density of the returned mud mixture 52 from Equation (2), ρ_(mud) is the density of the mud 36 routed to the BHA 24, ρ_(cuttings) is the density of the returned cuttings 48, Q_(mud) is the volumetric flow rate of the mud 36 into the wellbore 22, ROP_(log) is the lagged rate of penetration, and A_(wellbore) is the drilled hole area at the end 26 of the wellbore 22. In some embodiments, a gauge hole area may be assumed (i.e., no washout assumption). The flow rate Q_(mud) of the mud 36 and the ROP_(log) may be determined and/or controlled at the surface. For example, the flow rate Q_(mud) may be based on a speed or throughput of the mud pump 38. Additionally, or in the alternative, the ROP_(log) may be determined for a time t from a log of ROP during the drilling operation. A cleaning efficiency ratio η value greater than 1.0 may indicate a washout condition, and cleaning efficiency ratio η value less than 1.0 may indicate an accumulation of cuttings 48 within the wellbore 22.

In some embodiments, the ROP_(log) represents the rate of penetration producing cuttings at time t, which is sensed by the load cell 104 at time t+T, where Tis the lag for the cuttings to travel from downhole to the duct 56. The value T may be determined from Equation (5):

$\begin{matrix} {T = \frac{{A_{ann}*L_{ann}} + A_{{return}*L_{return}}}{Q_{mud}}} & {{Equation}\mspace{14mu} (5)} \end{matrix}$

where A_(ann) is the average annulus cross-section of the wellbore 22, L_(ann) is the annulus length at time t, A_(return) is the cross-section of the return line 54, and L_(return) is the length that the returned mud mixture 52 traveled through the wellbore 22 to the duct 56. For example, the lag T for generated cuttings to be lifted to the surface may be up to 10, 30, 60, 300, or 600 seconds or longer. The ROP_(log) may be based on the depth of the wellbore 22, properties of the riser 12 (e.g., strength, elasticity), a progression of the drill string 19 through the drilling system 30 at the surface, among others. Furthermore, the ROP_(log) may increase with the depth of the wellbore 22. Returning to Equation (4), in some embodiments, the density ρ_(cuttings) of the returned cuttings 48 may be determined with logging while drilling (LWD) data. In some embodiments, the controller 140 may determine the density ρ_(cuttings) of the returned cuttings 48 from Equation (6):

$\begin{matrix} {\rho_{cuttings} = {\frac{m_{cuttings}}{v_{cuttings}} = \frac{\left( {m_{mixture} - m_{mud}} \right)}{\left( {v_{mixture} - \frac{m_{mud}}{\rho_{mud}}} \right)}}} & {{Equation}\mspace{14mu} (6)} \end{matrix}$

where v_(mixture) is the volume of the quantity 106 of the returned mud mixture 52. If the v_(mixture) and/or the density ρ_(cuttings) of the returned cuttings 48 are not known in advance by the controller 140, then the following Equation (7) may be used to compute a change σ in the cleaning efficiency ratio η over time (i.e., between t₁ and t₂):

$\begin{matrix} {\sigma = {\frac{\eta \left( t_{2} \right)}{\eta \left( t_{1} \right)} = {\frac{\rho_{{{mixture}{(t_{2})}} - \rho_{mud}}}{\rho_{{{mixture}{(t_{1})}} - \rho_{mud}}}*\frac{{Q_{mud}\left( t_{2} \right)}*{{ROP}_{lag}\left( t_{1} \right)}}{{Q_{mud}\left( t_{1} \right)}*RO{P_{lag}\left( t_{2} \right)}}}}} & {{Equation}\mspace{14mu} (7)} \end{matrix}$

The controller 140 may determine the cleaning efficiency ratio η dynamically during a drilling operation. For example, the controller 140 may determine the cleaning efficiency ratio η continuously, or at intervals such as 5, 15, 30, 60, or 300 seconds or more. In some embodiments, the controller 140 may average or weight the determined cleaning efficiency ratio η values over time to determine trends of the cleaning efficiency ratio. For example, the controller 140 may decrease the mud flow rate or the viscosity of the mud 36 in response to a determined cleaning efficiency ratio η of 1.1 or 1.2. Additionally, rapid increases in the determined cleaning efficiency ratio η beyond 1.1 may indicate a washout condition. Accordingly, the controller 140 may decrease the mud flow rate and/or the viscosity of the mud 36 to slow or halt the washout condition within the wellbore 22. The controller 140 may continue to monitor the cleaning efficiency ratio η and adjust additional parameters of the drilling operation to improve the cleaning efficiency ratio η. Moreover, increasing the mud density may increase the ROP, which could increase the cleaning efficiency ratio η. In a similar manner, decreasing the mud density may decrease the ROP, which could decrease the cleaning efficiency ratio In some embodiments, the controller 140 may increase the mud flow rate and/or the viscosity of the mud 36 to increase the removal of cuttings 48 from the wellbore in response to a determined cuttings accumulation condition if the determined cleaning efficiency ratio η is less than 1.0. One or more of the parameters of the drilling operation that affect the cleaning efficiency ratio η include the mud flow rate, the mud density, the mud composition (e.g., viscosity, additives), the weight on the bit (WOB), the top drive system speed, the ROP of the drill string, and a start/stop condition for the drilling operation.

In some embodiments, the controller 140 may control a parameter of the drilling system 30 based on the cleaning efficiency ratio η if the determined cleaning efficiency ratio η is outside of a threshold range (e.g., 0.05 to 0.1) of 1.0 for a threshold period, such as 15, 30, 60, 100, or 300 seconds or more. In some embodiments, the controller 140 that determined the cleaning efficiency ratio η also controls the one or more parameters of the drilling operation to tune the cleaning efficiency ratio toward 1.0. In some embodiments, the controller 140 provides the determined cleaning efficiency ratio values to another controller and/or to an operator that controls the one or more parameters of the drilling operation. That is, the controller 140 may provide an alert or notification associated with the determined cleaning efficiency ratio

FIG. 4 illustrates an embodiment of the mud monitoring system 32 between the riser 12 and the mud processing system 34 with a different configuration of the measuring device 102. A section 148 of the duct 56 may be supported by load cells 150, 152, and the quantity 106 of the returned mud mixture 52 monitored by the mud monitoring system 32 is the totality of the returned mud mixture 52 within the section 148. In some embodiments, the load cells 150, 152 support the first end 94 and the second end 96 of the duct 56. The first end 94 may offset above the second end 96 by the elevation 98. Sensor feedback from the load cells 150, 152 may reflect the weight of the section 148 of the duct 56 and the mass m_(quantity) of the quantity 106 of the returned mud mixture 52 within the section 148. The section 148 may be all or a fraction of the length 100 of the duct 56 between the load cells 150, 152. In some embodiments, the section 148 of the duct 56 may be a portion that is supported by the load cells 150, 152 between flexible connections (e.g., bellows) that facilitate movement of the section 148 along the vertical axis 68 while the ends 94, 96 of the duct 56 are fixedly supported by the platform of the drilling system.

The density of the returned mud mixture 52 may be determined from the mass of the quantity 106 of the returned mud mixture 52 via the load cells 150, 152 and the volume of the quantity 106. One or more mud level sensors 154 may be used to determine a depth of the returned mud mixture 52 at positions along the section 148. Where the shape of the duct 56 along the section 148 is known, the depth of the returned mud mixture 52 from the one or more mud level sensors 154 may be used to determine the volume of the quantity 106 within the section 148. Accordingly, the controller 140 may determine the density of the returned mud mixture 52 via sensor feedback from the load cells 150, 152 and the mud level sensors 154. The one or more mud level sensors 154 may include, but are not limited to ultrasonic sensors, microwave sensors, capacitance sensors, float sensors such as the paddle 124 and the potentiometer 132 described above with FIG. 3, and so forth. The controller 140 may determine the volume of the quantity 106 within the section 148 based on the feedback from the one or more mud level sensors 154. In some embodiments, the controller 140 may use data (e.g., lookup table, calibration data, etc.) within the memory 144 and the determined depth of the returned mud mixture 52 at one or more locations of the section 148 to determine the volume of the quantity 106.

In some embodiments, the mud monitoring system 32 may measure the quantity 106 of the returned mud mixture 52 within the return line 54 rather than within the duct 56. FIG. 5 illustrates an embodiment of the mud monitoring system 32 configured to monitor the quantity 106 of the returned mud mixture 52 within a portion 170 of the return line 54. The return line 54 may be a closed duct, as illustrated in FIG. 5. In some embodiments, arranging the measuring device 102 with the return line 54 may reduce the size of the duct 56 or enable the elimination of the duct 56 on the platform of the drilling system. That is, the return line 54 may provide the returned mud mixture 52 directly to the mud processing system 34 via the drain 58. The measuring device 102 of the mud monitoring system 32 may include the load cell 150 configured to support the portion 170 of the return line 54 and the returned mud mixture 52 between bellows 172. The load cell 150 is configured to provide feedback to the controller 140 based on the weight of the portion 170 of the return line 54 and the mass m_(quantity) of the quantity 106 of the returned mud mixture 52 within the portion 170. The bellows 172 may provide flexibility of the return line 54 along the vertical axis 68 while facilitating the measurement of the quantity 106 of the returned mud mixture 52. In some embodiments, the bellows 172 enable some lateral movement of the portion 170 of the return line 54 relative to the fixed portions 173. In some embodiments, the return line 54 is a closed conduit, as illustrated in FIG. 5. An upstream end 174 of the return line 54 may be disposed at the same or higher elevation along the vertical axis 68 than a downstream end 176 of the return line 54, thereby facilitating flow of the returned mud mixture 52 through the return line 54. The mud level sensor 108 may be arranged at least partially within the portion 170 of the return line 54. As discussed above, one or more mud level sensors 108 may provide feedback to the controller 140 about a depth 130 of the returned mud mixture 52 at the position 116 of the portion 170. Based on the feedback from the one or more mud level sensors 108, the controller 140 may determine a volume of the quantity 106 of the returned mud mixture 52. As discussed above, the controller 140 may determine the mass of the quantity 106 via feedback form the load cell 150 coupled to the portion 170. The controller 140 may then determine the density of the returned mud mixture 52 based on the volume of the quantity 106 and the mass of the quantity 106. Furthermore, with the density of the returned mud mixture 52, the controller 140 may determine the cleaning efficiency ratio η during the drilling operation.

In some embodiments, the mud monitoring system 32 may have a bypass section 180 to determine the density of the returned mud mixture 52 within a fixed volume of the bypass section 180, as illustrated in FIG. 6. The bypass section 180 may receive a portion 182 of the returned mud mixture within the return line 54. For example, a funnel 184 may be arranged within the return line 54 to divert the portion 182 into the bypass section 180. The bypass section 180 directs the portion 182 of the returned mud mixture 52 to a bypass conduit 186 supported between bellows 172. The bypass conduit 186 is more narrow than the bypass section 180, such that the bypass conduit 186 is filled with the returned mud mixture 52. The load cell 150 may determine the weight of the bypass conduit 186 and the mass m_(quantity) of the quantity 106 of the returned mud mixture 52 within the bypass conduit 186, then determine the mass of the quantity 106. The volume within the bypass conduit 186 may be a fixed volume known to the controller 140 without the one or more mud level sensors described above. Because the bypass conduit 186 is filled with the returned mud mixture 52, the controller 140 may determine the density of the quantity 106 of the returned mud mixture 52 within the bypass conduit 186 without a mud level sensor 108. In some embodiments, the quantity of the returned mud mixture 52 of the fixed volume of the bypass section 180 may be greater than the quantity measured by the load cell 104 of the open duct 96 of FIG. 3, thereby increasing the sample size for determination of the density of the returned mud mixture 52.

The bypass section 180 and the bypass conduit 186 with the load cell 150 may enable the controller 140 to determine the density of the quantity 106 of the returned mud mixture 52 despite an inclination of the bypass conduit 186 relative to the vertical axis 68 between the bellows 172, as shown in FIG. 6. Accordingly, the embodiment of the mud monitoring system 32 with the bypass section 180 may have a smaller footprint on a platform of the drilling system 30 than the mud monitoring system 32 with the duct 56 described above with FIG. 3. A remainder 188 of the returned mud mixture 52 not diverted by the funnel 184 and the portion 182 of the returned mud mixture 52 from the bypass conduit 186 may be directed to the mud processing system 34, such as via the drain 58.

As described above, the controller 140 of the mud monitoring system 32 may utilize feedback from the measurement device 102 to determine the cleaning efficiency ratio during the drilling operation. FIG. 7 illustrates an embodiment of a method 200 that the controller 140 may utilize to monitor the returned mud mixture to determine the cleaning efficiency ratio η and control the drilling operation based on the determined cleaning efficiency ratio η. In some embodiments, the processor 142 of the controller 140 may execute instructions (e.g., code, software) stored in the memory 144 (e.g., non-transitory, computer readable media) to perform one or more steps of the method 200. Additionally, data stored in the memory 144 of the controller 140 and/or received from other controllers of the drilling system 30 may be utilized by the controller 140 to perform one or more steps of the method 200.

As discussed above, the mud monitoring system monitors the returned mud mixture at the surface of the drilling system between the riser and the mud processing system. The controller determines (block 202) a mass of the quantity of the returned mud mixture. The controller may utilize sensor feedback from one or more load cells of the mud monitoring system, as described above with FIGS. 3-6. In some embodiments, the controller may determine (block 202) the mass of the quantity of the returned mud mixture directly, as described above with Equation (1) and FIG. 3. In some embodiments, the controller may determine (block 202) the mass of the quantity of the returned mud mixture indirectly, such as via measuring a weight of the duct with the quantity of the returned mud mixture and subtracting the weight of the duct itself.

In some embodiments, the controller determines (block 204) the volume of the quantity of the returned mud mixture. For example, the controller may utilize sensor feedback from a mud level sensor at a position and the cross-sectional geometry of the duct at the position to determine the volume of the quantity at the position. In some embodiments, the controller may utilize sensor feedback from multiple mud level sensors at different respective positions to determine (block 204) the volume of the measured quantity of the returned mud mixture. The one or more mud level sensors may include ultrasonic sensors, microwave sensors, capacitance sensors, float sensors, or any combination thereof. The controller may associate the determined volume at the position with the volume of the quantity of the returned mud mixture. In some embodiments, as described above with FIG. 6, the quantity of the returned mud mixture may have a fixed volume that may be stored in the memory of the controller. Furthermore, in some embodiments, it is appreciated that the controller may determine the volume (block 204) of the quantity of the returned mud mixture prior to or while determining the mass (block 202) of the quantity of the returned mud mixture.

The controller may determine (block 206) the density of the returned mud mixture based on the determined mass of the quantity of the returned mud mixture and the determined volume of the quantity of the returned mixture. For example, the controller may determine the density of the quantity of the returned mud mixture from the determined mass and volume of the quantity of the returned mud mixture, as described above with Equation (2). With the determined density of the returned mud mixture, the controller may determine (block 208) the cleaning efficiency ratio such as described above with Equation (4). The determined cleaning efficiency ratio η may incorporate a lag associated with the time for the generated cuttings to be lifted to the surface via the returned mud mixture 52. An accumulation of cuttings within the wellbore may be indicated by a cleaning efficiency ratio η less than 1.0, and a washout condition near the BHA may be indicated by a cleaning efficiency ratio η greater than 1.0. The controller may continuously or periodically determine the cleaning efficiency ratio η.

In some embodiments, the controller communicates (block 210) the determined cleaning efficiency ratio η and/or a trend of the determined cleaning efficiency ratio η over a sample period to an operator and/or to another controller of the drilling system. For example, the controller communicates the determined cleaning efficiency ratio η to a display for an operator of the drilling system. In some embodiments, the controller communicates the determined cleaning efficiency ratio η to a controller for the mud pump, the top drive system, the mud processing system, or any combination thereof. The controller of the mud monitoring system or another controller of the drilling system may control (block 212) one or more parameters of the drilling operation based on the determined cleaning efficiency ratio η. For example, the one or more parameters of the drilling system may be adjusted to seek maintenance of the cleaning efficiency ratio η at approximately 1.0. In some embodiments, the mud flow rate and/or the mud viscosity drilling parameters may be increased to increase the removal of cuttings from the wellbore and reduce the accumulation of cuttings within the wellbore. Additionally, or in the alternative, the ROP and the WOB may be decreased to lower the production of cuttings in the wellbore, thereby aiding to reduce the accumulation of cuttings and tune the cleaning efficiency ratio η towards 1.0. In some embodiments, the mud flow rate and the mud viscosity, may be decreased if the cleaning efficiency ratio η is greater than 1.0. It is appreciated that prior to increasing the cleaning efficiency ratio η to 1.0, the one or more drilling parameters may be controlled such that the cleaning efficiency ratio η is greater than 1.0 for a cleaning period so that the accumulated cuttings may be removed from the wellbore. The one or more drilling parameters that may be controlled (block 212) based on the determined cleaning efficiency ratio η may include, but are not limited to the mud flow rate of the mud directed to the wellbore, the mud density of the mud routed into the wellbore, the mud composition (e.g., viscosity, additives), the WOB, the top drive system speed, the ROP of the drill string, and a start/stop condition for the BHA.

The technical effects of the mud monitoring system described above include determination of the cleaning efficiency ratio during the drilling operation. The arrangement of the mud monitoring system between the riser and the mud processing system may enable the components of the mud monitoring system to be maintained, calibrated, and/or replaced more easily than sensors upstream of the return line, such as within the drill string. Furthermore, through measurement of the density of the returned mud mixture within the return line or the duct of the mud monitoring system, the effects of multiple phases (e.g., liquids, gases, solids) on the measurement of the returned mud mixture may be reduced.

This written description uses examples to disclose the above description, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Additionally, the usage herein of the term approximately with given values includes values within 10 percent of the given values. Accordingly, while the above disclosed embodiments may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the embodiments are not intended to be limited to the particular forms disclosed. Rather, the disclosed embodiment are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the embodiments as defined by the following appended claims. 

What is claimed is:
 1. A system comprising: a measuring device configured to receive a returned mud mixture from a riser and to direct the returned mud mixture to a mud processing system, wherein the measuring device comprises: a duct comprising a first end disposed at a first level and a second end disposed at a second level, wherein the first level is higher than the second level along a vertical axis; a first load cell coupled to the duct, wherein the first load cell is configured to determine a mass of a quantity of the returned mud mixture within the duct during a drilling operation; and a mud level sensor configured to determine a height of the returned mud mixture in the duct.
 2. The system of claim 1, wherein the duct comprises a trough with a length between the first end and the second end, and the first load cell is disposed at a first position from the first end that is greater than or equal to 25 percent of the length.
 3. The system of claim 1, wherein the first load cell is disposed at a first position from the first end, and the mud level sensor is disposed at a second position from the first end, and the first position is different from the second position.
 4. The system of claim 3, wherein the mud level sensor is configured to determine the height of the returned mud mixture in the duct at the first position based on a second height of the returned mud mixture in the duct at the second position.
 5. The system of claim 1, wherein the measuring device comprises a second load cell, wherein the first load cell is coupled to the duct near the first end, the second load cell is coupled to the duct near the second end, and the quantity of the returned mud mixture comprises a totality of the returned mud mixture within the duct.
 6. The system of claim 1, wherein the duct comprises a return line coupled to the riser, wherein the return line comprises a first baffle, a second baffle, and a portion coupled between the first baffle and the second baffle, wherein the first load cell is coupled to the portion, the first load cell is configured to support the portion of the duct along the vertical axis, and the quantity of the returned mud mixture comprises a volume of the returned mud mixture within the portion.
 7. The system of claim 1, comprising a controller coupled to the first load cell and to the mud level sensor, wherein the controller is configured to determine, during the drilling operation, a cleaning efficiency ratio of the drilling operation based on a first feedback from the first load cell and a second feedback from the mud level sensor.
 8. The system of claim 1, wherein the mud level sensor comprises a paddle and a potentiometer.
 9. The system of claim 1, wherein the mud level sensor comprises one or more non-contact sensors.
 10. The system of claim 1, comprising the mud processing system configured to receive the returned mud mixture from the second end of the duct, and the mud processing system comprises a shaker table, mud cleaning equipment, or any combination thereof
 11. A system comprising: a measuring device configured to receive a returned mud mixture from a riser and to direct the returned mud mixture to a mud processing system, wherein the measuring device comprises: a duct comprising a first end and a second end, wherein the first end is configured to receive a quantity of the returned mud mixture, and the second end is configured to direct the quantity of the returned mud mixture to the mud processing system; and a load cell coupled to the duct, wherein the load cell is configured to determine a mass of the quantity of the returned mud mixture within the duct during a drilling operation.
 12. The system of claim 11, wherein the measuring device comprises a funnel disposed in a return line, wherein the funnel is configured to divert a portion of the returned mud mixture into a bypass section, wherein the duct comprises the bypass section, and the bypass section is filled with the quantity of the returned mud mixture during the drilling operation.
 13. The system of claim 12, wherein the measuring device comprises a first baffle and a second baffle, the bypass section is disposed between the first baffle and the second baffle, and the load cell is coupled to the bypass section.
 14. The system of claim 13, comprising a controller coupled to the load cell, wherein the controller is configured to determine a density of the quantity of the returned mud mixture in the bypass section based at least in part on a volume of the bypass section and a feedback of the load cell.
 15. The system of claim 14, wherein the controller is configured to determine, during the drilling operation, a cleaning efficiency ratio of the drilling operation based on the density of the quantity of the returned mud mixture in the bypass section.
 16. The system of claim 11, comprising a controller coupled to the measuring device, wherein the measuring device comprises a mud level sensor disposed within the duct, the mud level sensor is configured to determine a height of the returned mud mixture within the duct at a position of the load cell, and the controller is configured to determine, during the drilling operation, a cleaning efficiency ratio of the drilling operation based on first feedback from the load cell and a second feedback from the mud level sensor.
 17. A method comprising: determining a mass of a quantity of a returned mud mixture in a duct disposed between a riser and a mud processing system of a drilling platform; determining a mixture density of the quantity of the returned mud mixture based on the mass of the quantity of the returned mud mixture and a volume of the quantity of the returned mud mixture; determining, during the drilling operation, a cleaning efficiency ratio of a drilling operation based at least in part on the mixture density of the quantity of the returned mud mixture and a mud density of a drilling mud supplied to a wellbore during the drilling operation; and controlling one or more parameters of the drilling operation based at least in part on the cleaning efficiency ratio of the drilling operation, wherein the controlled one or more parameters of the drilling operation comprise a flow rate of the drilling mud, a composition of the drilling mud, a weight on a bit of the drilling platform, or any combination thereof
 18. The method of claim 17, comprising determining the volume of the quantity of the returned mud mixture based on feedback from a mud level sensor coupled to the duct.
 19. The method of claim 17, comprising: decreasing the flow rate of the drilling mud when the cleaning efficiency ratio is greater than 1.0; and increasing the flow rate of the drilling mud when the cleaning efficiency ratio is less than 1.0.
 20. The method of claim 17, comprising determining the mass of the quantity of the returned mud mixture based on feedback from a plurality of load cells coupled to the duct. 